1. Field of the Invention
The invention relates to a device for sensing the front edge or the end edge of a recording material carrier in a processing apparatus including a feeler probe lever, which feeler probe lever rests on the spring-supported switching element of a microswitch and of an electronic control or display circuit connected to the connection contacts of the microswitch.
2. Brief Description of the Background of the Invention Including Prior Art
Such sensing devices for sensing the front edge or the end edge of a recording material carrier serve for recognizing of recording material carriers such as paper sheets, paper tapes, continuous unrolled paper and their position, in order to initiate a certain printing or processing step. In addition, the absence of the recording material carrier is registered.
Optical sensors are conventionally employed for recognizing the front edge of the paper. The optical sensors operate either according to the transmission or reflex principle. These optical sensors are associated with the disadvantage of requiring particular equipment and thus result in expensive adjustments depending on the optical spectrum of the surface of the paper material to be sensed. Extraordinary difficulties occur in case of transparent and colored recording material carriers. The adjustment of the different kinds of recording material carriers is further made more difficult by a possible presence of extrinsic light irradiation and by temperature increases occurring during apparatus operation and by deposits of dust.
In addition, according to the state of the art, a sensing lever is employed on a controlled tiltable frame for recognition of the recording material carrier front edge, which sensing lever cooperates with a light barrier or with an inductively acting transmitter pick-up device (Mannesmann-Kienzle Printer D 245). Such sensor devices based on a sensing lever construction act on optical or, respectively, inductive transmitter pick-up devices and are indeed reliable. However, these sensor devices require more equipment, in particular based on the separately controlled pivotable frame, and are relatively expensive in their production.
It is further known from German Patent Application Laid Open DE-OS 2,943,241 to construct a paper end switching device for a printer based on a feeler sensor subjected to a top load exerted by a lever sitting on top of the paper path, which lever is tiltable at one end around an axis parallel to the paper path and cross to the transport direction. An iron switching strip is disposed on the side of the paper path disposed opposite to the lever, which switching strip is pivotable around a pivot axis disposed parallel to the lever axis based on the effect and operation of the moving and extending lever against the action of a spring, wherein the switching strip actuates by the pivoting motion a switch of the printer. The lever carries a permanent magnet at its other rear end relative to the transport direction, which permanent magnet has one pole face directed toward the input side tilting part of the switching strip, and the one pole face of the permanent magnet can be set onto the input side pivoting part in a pivoting position of the switching strip by tilting of the lever in transport direction of a passed through continuous paper. In the pivot position of the switching strip the input side pivot part is pivoted in the direction of the permanent magnet under the effect and interaction of the permanent magnet. Such a paper end switching device is not only equipment-requiring but does also not contribute anything to a precise determination of the position of a front edge or of a rear end edge of a recording material carrier.